1. Field of the Invention
This invention relates to a magnetic recording apparatus, and more particularly to a magnetic recording apparatus employing an IDless scheme where a data sector begin mark, data sector address information, etc. are not recorded at the head of each data sector, which is a recording unit of a recording medium.
2. Description of the Related Art
With a conventional magnetic recording apparatus, especially a magnetic disk apparatus, when the data is read, the head is positioned on the track where the target data sector to be read is present and then the target data sector is searched for and read.
In a magnetic disk apparatus employing an IDless scheme where a data sector begin mark, data sector address information, etc. are not recorded at the head of each data sector, which is a recording unit of a recording medium (disk), the read/write head scans over the track and senses a servo sector located before the target data sector (a servo sector address is read). By counting the data sector pulses generated with the timing based on the format table on the ROM (Read Only Memory) from when the servo sector has been sensed to when the counting reaches the number corresponding to the target data sector, the timing that the target data sector passes under the head is obtained. This enables the target data sector to be sensed (the data in the data sector is read).
When a servo sector is sensed, however, if the disk has dust on it or a flaw in it or the head is interfered with by noise, the servo sector address will not be read. In this case, it is only natural that the target sector cannot be sensed.
Should this happen, the settings of various parameters including filter constants will be changed and the sensing of the same servo sector will be tried. When the servo sector cannot be sensed no matter how many times the sensing has been tried, however, the sensing of the target data sector has to be abandoned.